1. Field of the Invention
The present invention relates to an electrically operated steering apparatus for steering steerable vehicle wheels, such as front wheels or rear wheels, with assistive steering forces generated by an electric motor.
2. Description of the Related Art
Conventional electrically operated power steering apparatus for motor vehicles have a rack shaft for steering steerable wheels and an electric motor positioned in the vicinity of the rack shaft for actuating the rack shaft to generate and apply assistive steering forces to the steerable wheels. The rack shaft and the electric motor are accommodated in a housing located outside of the cabin of the motor vehicle. A power supply, typically a vehicle-mounted battery, for energizing the electric motor is also positioned outside of the cabin. The conventional electrically operated power steering apparatus also have a motor driver circuit comprising power electronic devices such as field-effect transistors (FET) or the like and a motor control circuit for controlling the motor driver circuit based on a detected steering torque. The motor driver circuit and the motor control circuit are positioned in the cabin, and electrically connected to the electric motor in the housing and the power supply by wire harnesses.
With the recent advances in the electronic component technology, electronic components for use in the motor driver circuit and the motor control circuit have become more and more reliable, i.e., have had a longer service life and a higher performance capability. The availability of such reliable electronic components makes it possible for the motor driver circuit and the motor control circuit to be positioned under adverse conditions in the vicinity of the housing which accommodates the rack shaft and the electric motor. The motor driver circuit and the motor control circuit are encased in a water-resistant, humidity-resistant, and vibration-resistant structure and electrically connected to the electric motor and the power supply by wire harnesses. Since a large current is supplied from the power supply to energize the electric motor, the wire harnesses are required to be highly resistant to heat, covered with a thick sheath, and have a high current carrying capacity.
The wire harnesses are connected to the electric motor in the housing, the power supply, the motor driver circuit, the motor control circuit through joints that are protected by water-resistant seals in the form of rubber grommets.
Because the wire harnesses with a high current carrying capacity are drawn directly into the housing for connection to the electric motor, it has been tedious and time-consuming to place the wire harnesses in position and fix them with the grommets.
The protective water-resistant seals or grommets used to protect the joints outside of the cabin pose problems on the ease with which the electrically operated power steering apparatus can be assembled and serviced for maintenance.